1. Field of the Invention
Example embodiments of the present invention relate to a method of forming a thin layer, and more particularly relate, for example, to a method of forming a thin layer having a single-crystal structure.
2. Description of the Related Art
Solid materials may be classified into three categories, for example, single-crystal material, poly-crystalline material and amorphous material depending upon the structure thereof. The single-crystal material may have a regular unit crystal structure, e.g., an arrangement which may be regular. In contrast, the poly-crystalline material may have a plurality of unit crystal structures, each of which may have an irregular and/or random arrangement. The amorphous material may have no crystal structure, and the atoms may be irregularly arranged therein.
The poly-crystalline material may contain many grain boundaries due to the various (e.g., many) unit crystal structures thereof, each of which may be aligned in different directions. Such alignment in the various different directions may hinder carriers such as electrons and holes from moving and/or being controlled in the poly-crystalline material. This may lead to a deterioration of electronic characteristics of the poly-crystalline material. In contrast, the single-crystal material may have almost no grain boundaries due to the single-crystalline structure. Accordingly, the carriers may move relatively freely and may be more readily controlled in the single-crystal material than in the poly-crystalline material. As a result, the electronic characteristics of the single-crystal material should be superior to those of the poly-crystalline material.
For the above reason, a stacked structure such as a thin-film transistor (TFT) or a multilayer structure such as a system-on-chip (SOC) device may include at least one structure comprising a single-crystal material as a channel layer thereof. An example of a single-crystal material may include a single-crystalline silicon layer.
An amorphous silicon layer may be formed on a single-crystalline silicon layer. An epitaxial process may be conducted on the amorphous silicon layer using the underlying single-crystal structure in the silicon layer as a seed. Accordingly, the structure of the amorphous silicon layer may be transformed into a single-crystal structure, thereby forming and/or growing the single-crystalline silicon layer.
A native oxide layer may often form on a surface of a single-crystalline silicon thin layer. The native oxide layer may cause some problems in forming an amorphous silicon layer on a single-crystalline silicon thin layer. For example, when an epitaxial process is conducted on an amorphous silicon layer formed on a single-crystalline silicon thin layer having a native oxide layer, nucleation may be randomly generated on a surface of the amorphous silicon layer. This may be because the native oxide layer may prevent (or interfere with) the single-crystalline silicon in the single-crystalline silicon thin layer from being used as the seed in the epitaxial process. Accordingly, the amorphous silicon layer may be transformed into a poly-crystalline silicon layer rather than a single-crystalline silicon layer during or as a result of the epitaxial process conducted.
In view of the above, the formation of the native oxide layer has been an obstacle in transforming the amorphous silicon layer into the single-crystalline silicon layer.
Thus, various methods have been suggested for removing and/or preventing the formation of the native oxide layer on the single-crystalline silicon thin layer so as to more readily permit transformation of an amorphous silicon layer into a single-crystalline silicon layer. For example, under high vacuum conditions in a processing chamber (for forming the amorphous silicon layer), a residual amount of vapor (H2O) and oxygen (O2) gas may be reduced sufficiently to prevent the formation of the native oxide layer. Further, ion beams may be applied onto a surface of the amorphous silicon layer, so that the native oxide layer may be removed. However, these methods require additional devices for evacuating the processing chamber and for projecting ion beams.
According to conventional art, an insulation pattern may be formed on a single-crystalline silicon thin layer in which a single-crystalline silicon may be used as a seed in the epitaxial process, and the single-crystalline silicon thin layer may be partially exposed to the epitaxial gases. For example, a silicon source gas may be supplied onto the single-crystalline silicon thin layer (including the insulation pattern), to prevent the native oxide layer from forming on the single-crystalline silicon thin layer. Accordingly, an epitaxial layer may be formed on the single-crystalline silicon thin layer, and an amorphous silicon layer (without the native oxide layer) may be formed on the insulation pattern.
However, a thinning defect may be created at a boundary portion between the insulation pattern and the single-crystalline silicon thin layer, as shown in FIG. 1. FIG. 1 depicts a thinning defect at the boundary portion between the insulation pattern and the single-crystalline silicon thin layer.
Referring to FIG. 1, the thickness of the amorphous silicon layer is thinner at the boundary portion I between the insulation pattern and the single-crystalline silicon thin layer because the chemical bond energy is greater between the silicon source gas and the single-crystalline silicon thin layer versus that between the silicon source gas and the insulation pattern. Most of the silicon source gases supplied to the boundary portion I react with the insulation pattern rather than with the single-crystalline silicon thin layer due to the higher bond energy associated with the single-crystalline silicon thin layer.
When a subsequent process such as a chemical mechanical polishing (CMP) process or an etching process is conducted on the amorphous silicon layer subject to the thinning defect, the amorphous silicon layer may be more readily (and possibly frequently) broken at the boundary portion I due to the thinning defect.